1. Technical Field
The present invention relates to a vehicle occupant protection apparatus and, in particular, to an inflator for an inflatable vehicle occupant protection device, such as an air bag.
2. Description of the Prior Art
European Patent Application EP 0 903 487 A2 describes an integrated pulsed propulsion system for a microsatellite and, in particular, a microthruster for a microsatellite. The microthruster is formed with a chamber closed by a diaphragm, which acts as a blow-out disk. A fluid, such as an inert gas, is disposed within the chamber. Heating of the gas causes the gas pressure to increase until the diaphragm ruptures, which, in turn, causes the gas to flow out of the chamber. The flowing gas acts as a propellant, and provides a small unit of force. The microthruster is adapted to be formed by known batch processing methods with 104 to 106 microthrusters per wafer. The unit of force can be scaled by varying the number of microthrusters used for an application, the geometry of the chamber, and the type of fluid used within the chamber.
The microthruster described in EP 0 903 487 A2 is described elsewhere in the literature as consisting of a 3-layer sandwich. The top layer contains an array of thin diaphragms (0.5 micron thick silicon nitride, 190 or 290 or 390 microns square). The middle layer contains an array of through-holes (Schott FOTURAN(copyright) photosensitive glass, 1.5 mm thick, 300, 500, or 700 micron diameter holes), which are loaded with propellant. The bottom layer contains a matching array of polysilicon micro-resistors. The bottom two layers are bonded together, propellant is added to the middle layer, then the top layer is bonded to complete the assembly. With different sizes of plenum holes, diaphragms, and resistors, many different configurations can be assembled.
This type of microthruster is one type of device known in the art as a xe2x80x9cmicroelectromechanical system devicexe2x80x9d, or xe2x80x9cMEMS devicexe2x80x9d. This type of device is known for use in a variety of applications. For example, U.S. Pat. No. 5,880,921 discloses a monolithically integrated switched capacitor bank using MEMS technology.
The present invention is an actuatable inflator for an inflatable vehicle occupant protection device. The inflator comprises an assembly comprising a plurality of individually energizable microelectromechanical system (MEMS) devices for, when energized, actuating the inflator. The assembly further comprises a sensor mechanism for sensing a condition of the inflator and for generating a control signal indicative of the sensed condition. The plurality of MEMS devices are responsive to the control signal to control actuation of the inflator.